The present invention is directed to a drive bogie for a crawler vehicle, the bogie comprising carrying wheels which are freely rotatably suspended from a solid or divided bogie beam, with an endless crawler mat passing over the carrying wheels. At least one drive roll is provided, which drives the crawler mat and which is disposed so as to press the crawler mat between the roll and the carrying wheels, e.g. from above.
The use of a crawler mat in "off-the-road" vehicles and equivalent is known in and of itself. On the one hand, attempts have been made by the use of such a crawler mat, to improve the tractive capacity of the vehicle over difficult terrain. On the other hand, attempts have been made by the use of such a crawler mat, to reduce surface pressure between the vehicle and the ground, in order to prevent the vehicle wheels from sinking too deeply into the ground. Thus, generally speaking, use of such crawler mats improves the running quality of an off-the-road vehicle over difficult terrain.
The most common arrangement in off-the-road vehicles, is an endless crawler mat being passed about the carrying wheels included in the bogie construction of the vehicle. As a rule, at least one of the carrying wheels has been arranged as a drive wheel. Another conventional drive arrangment is such that, in addition to the carrying wheels, the bogie construction is provided with a separate drive wheel which drives the crawler from inside the crawler mat. An example of such an arrangement is known, for example, from British patent No. 2,116,922.
Driving of a crawler mat from outside is also known, in and of itself, in bogie constructions. For example, in U.S Pat. No. 3,443,654, a vehicle bogie construction is disclosed in which the drive is passed by way of a cardan shaft to the bogie of a vehicle loader. A crawler mat is passed around the wheels in the bogie, with the mat being driven from outside by a drive wheel. The bogie wheels and the drive wheel are mounted on separate shafts. In this particular arrangement, the outer face of the crawler mat is provided with grasping rails, which the drive wheel can engage, thereby transmitting movement from the drive wheel to the crawler mat.
Additional bogie constructions in which the drive is explicitly arranged on the outer face of the crawler mat, are described in the prior art, for example in U.S. Pat. Nos. 3,447,620, 3,447,621; 3,533,482; 3,600,044; and 4,194,584.
Thus in prior art bogie constructions, for example in connection with forest tractors, it has been known to use two carrying wheels mounted on a bogie beam, in which at least one of the wheels is also a drive wheel. It is also known in the prior art to pass the drive to one wheel or to both wheels. The bogie is usually journalled at the middle of the wheels, at a point considerably higher than the center line between the wheels, in order to obtain adequate ground clearance, which is necessary under particular forest conditions.
The drive to the wheels may have been passed by way of a cogwheel transmission inside a box construction, from the journalling shaft of the bogie construction to the wheels. If a crawler mat passing around the wheels has been utilized, then the crawler mat has, as a rule, been driven from the inside. However, a drive from the outside has been known in the prior art, as is apparent, for example, from the above U.S. Pat. No. 3,443,654.
In connection with forest tractors, an arrangement has also been known in which the drive is provided so that a drive roll is pressed between the wheels mounted on the bogie beam, whereby the drive is transmitted from the drive roll directly to the carrying wheels, through the tires of the wheels.
However, the drive bogie arrangementsthat have been known in the prior art, have a complicated construction, and therefore the cost of manufacture is high. A further drawback of the prior art bogie constructions making use of a drive roll, is the unreliability of the drive under difficult conditions, as well as the constant loss of power and wear upon the tires, resulting from the necessary high compression force of the roll. The wear of the tires is highly extensive, especially when the drive roll is directly pressed against the tires of the carrying wheels.
The crawler mats used on the present-day bogie constructions are, almost without exception, formed to be non-extending and non-resilient in the direction of drive, i.e. in the running direction of the vehicle, because elasticity of a crawler mat is, in general, considered a drawback, especially in view of the tensioning and the guiding quality of the crawler mat. If the surface material of the crawler mat has been made of a resilient material, then the crawler mat has usually been made non-resilient by means of various draw or reinforcement layers, which have been vulcanized onto or into the surface layer. The structure of such a crawler mat principally resembles, for example, the structure of vehicle tires.